[CentOS] Slow RAID Check/high %iowait during check after updgrade from CentOS 6.5 -> CentOS 7.2
Gordon Messmer
gordon.messmer at gmail.com
Fri May 27 03:50:15 UTC 2016
On 05/25/2016 09:54 AM, Kelly Lesperance wrote:
> What we're seeing is that when the weekly raid-check script executes, performance nose dives, and I/O wait skyrockets. The raid check starts out fairly fast (20000K/sec - the limit that's been set), but then quickly drops down to about 4000K/Sec. dev.raid.speed sysctls are at the defaults:
It looks like some pretty heavy writes are going on at the time. I'm not
sure what you mean by "nose dives", but I'd expect *some* performance
impact of running a read-intensive process like a RAID check at the same
time you're running a write-intensive process.
Do the same write-heavy processes run on the other clusters, where you
aren't seeing performance issues?
> avg-cpu: %user %nice %system %iowait %steal %idle
> 9.24 0.00 1.32 20.02 0.00 69.42
>
> Device: tps kB_read/s kB_wrtn/s kB_read kB_wrtn
> sda 50.00 512.00 20408.00 512 20408
> sdb 50.00 512.00 20408.00 512 20408
> sdc 48.00 512.00 19984.00 512 19984
> sdd 48.00 512.00 19984.00 512 19984
> sdf 50.00 704.00 19968.00 704 19968
> sdg 47.00 512.00 19968.00 512 19968
> sdh 47.00 512.00 19968.00 512 19968
> sde 50.00 704.00 19968.00 704 19968
> sdj 48.00 512.00 19972.00 512 19972
> sdi 48.00 512.00 19972.00 512 19972
> sdk 48.00 512.00 19980.00 512 19980
> sdl 48.00 512.00 19980.00 512 19980
> md127 241.00 0.00 120280.00 0 120280
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